WO2008038527A1

WO2008038527A1 - Noble gas fluorescent lamp, lamp lighting device and liquid crystal display device

Info

Publication number: WO2008038527A1
Application number: PCT/JP2007/067908
Authority: WO
Inventors: Kiyoshi Hashimotodani; Masaki Hirohashi
Original assignee: Panasonic Corporation
Priority date: 2006-09-27
Filing date: 2007-09-14
Publication date: 2008-04-03
Also published as: JP4118944B2; JPWO2008038527A1; US20090046223A1

Abstract

A fluorescent lamp (10) is provided with a light emitting tube (102), which has a phosphor film on the inner surface, is filled with a discharge gas and composed of a translucent material; a first internal electrode (101a) sealed at one end portion of the light emitting tube (102) for applying a high frequency rectangular alternating current voltage; a second internal electrode (101b), which is sealed at the end portion of the light emitting tube (102) on the opposite side to the first internal electrode (101a); and an external electrode (103) arranged along the longitudinal direction of the light emitting tube at a prescribed distance from the light emitting tube (102). Outside the fluorescent lamp (102), a capacitive internal charge discharging means (104) is electrically connected to the second internal electrode (101b).

Description

Specification

Noble gas fluorescent lamp, lamp lighting device and liquid crystal display device

Technical field

TECHNICAL FIELD [0001] The present invention relates to a discharge light source that does not use mercury! / And reduces the environmental load, and a lighting device that lights such a light source.

Background art

In recent years, with the progress of larger and thinner digital TVs, there has been a strong demand for larger LCD backlights. As a light source for liquid crystal backlights, research on solid-state light-emitting devices using light-emitting diodes and organic EL elements has progressed as a replacement for the cold cathode fluorescent lamps that have been used heavily, and some of them have been commercialized. However, from the viewpoints of luminous efficiency, lifetime characteristics, and cost, it is not yet possible to completely replace the cold cathode fluorescent lamp for the time being.

[0003] Fluorescent lamps use a low-pressure glow discharge using mercury, which is an environmental load substance, as an ultraviolet spring source for exciting a phosphor that is the main light emitting element. For this reason, from the viewpoint of environmental protection, development of a light source that has the same efficiency as current fluorescent lamps without using mercury is required.

In order to achieve the above object, a radiation source that efficiently emits ultraviolet rays having a wavelength (about 100 nm to about 300 nm) capable of effectively exciting and emitting phosphors is required. What is attracting attention as an ultraviolet radiation medium by discharge other than mercury is discharge plasma at a low or medium pressure (generally atmospheric pressure or less) mainly composed of rare gases. One photon of ultraviolet light is finally converted into one photon of visible light by the phosphor, and energy corresponding to the difference between the energy of ultraviolet light and the energy of visible light is lost. For this reason, it is desirable that the wavelength of ultraviolet rays obtained by discharge be close to that of visible light. This is promising because of the relatively long wavelength of the ultraviolet radiation emitted from the discharge plasma force mainly composed of xenon among rare gas discharges.

[0005] In the xenon discharge, in particular, an excimer (excimer) in which an excited xenon atom and a ground state xenon atom are bound instablely is released, 172 nm It is known that the efficiency of the broad radiation nearby is high. In general, excimer formation and radiation dissociation are particularly efficient in Norse afterglow. Therefore, V, a so-called dielectric barrier discharge, in which a dielectric layer serving as a charge barrier that cuts off current is provided between the electrode and the discharge space, is more expensive than normal glow discharge! Efficiency can be expected.

[0006] For this reason, as a rare gas fluorescent lamp using a rare gas discharge mainly composed of xenon, a configuration in which the glass tube wall of the arc tube is used as a dielectric layer serving as a charge barrier has been energetic in the past. Has been studied. As an example of such a configuration, the structure of a lamp disclosed in Patent Document 1 is shown in FIG.

FIG. 10 is a cross-sectional view of an arc tube of a rare gas fluorescent lamp using dielectric barrier discharge.

In FIG. 10, an external electrode 3 in which a conductive metal wire such as nickel is wound in a coil shape is provided on the outer surface of a light-transmitting arc tube 2 made of hard glass or the like having a phosphor film formed on the inner surface. It is. An inner electrode 1 of a cold cathode is hermetically sealed at one end of the arc tube 2. The arc tube 2 is filled with a rare gas mainly composed of xenon at a predetermined pressure. A high-frequency rectangular Norse voltage is applied between the internal electrode 1 and the external electrode 3. The outside of the external electrode 3 is covered with a translucent insulating tube 4 to insulate the rectangular pulse voltage from the surroundings.

[0008] During the operation of the lamp, a dielectric near discharge is generated between the internal electrode 1 and the external electrode 3 using the tube wall of the arc tube 2 as a charge barrier, and is efficiently generated from a rare gas such as enclosed xenon. It emits ultraviolet rays, which excites the phosphor layer to emit light.

Patent Document 1: Japanese Patent Laid-Open No. 2002-42737

Disclosure of the invention

Problems to be solved by the invention

In the case of the configuration as shown in FIG. 10, there is a problem that the luminance distribution in the longitudinal direction is not uniform when the entire length of the arc tube 2 is increased. That is, in a portion far from the internal electrode 1, the electric field strength sufficient to discharge the rare gas and generate ultraviolet rays having sufficient strength cannot be obtained, and the luminance is lowered. In order to avoid this, if the voltage applied to the internal electrode 1 is increased, the brightness at the part far from the internal electrode 1 will increase, but the discharge current will increase, and this will cause the discharge near the internal electrode 1 to contract. As a result, the ultraviolet radiation efficiency is lowered and the luminance is lowered. On the screen As a liquid crystal backlight for televisions that is required to have uniform brightness, it is a big problem that the luminance is not uniform in the longitudinal direction of the arc tube 2. In Patent Document 1, in order to avoid this, a means of changing the winding pitch of the external electrode 3 is taken. By narrowing the winding pitch in the vicinity of the inner electrode 1 where the luminance decreases and in the portion far from the inner electrode 1, the input power per unit length is increased locally, and the luminance of that portion is increased.

However, in this method, there is a problem that the efficiency as a whole is lowered by excessively supplying power particularly to a portion where the ultraviolet radiation efficiency near the internal electrode 1 is low. Also, it is necessary to keep the brightness uniform even when the length of the arc tube 2 is changed according to the screen size of the TV, or when the input power to the backlight changes due to dimming according to the screen. is there. It was extremely difficult to design such a winding pitch of the external electrode 3, and there was a lack of practical flexibility!

[0012] The present invention has been made to solve the above-described problems. Mercury has been developed so that the luminance distribution in the longitudinal direction can be made uniform even at a low driving voltage without lowering the luminous efficiency. Do not use! /, To provide a noble gas fluorescent lamp and its lighting device.

Means for solving the problem

The lamp lighting device according to the present invention is a lamp lighting device including a fluorescent lamp and a power supply circuit that supplies a driving voltage to the fluorescent lamp. The fluorescent lamp has a light-emitting tube made of a light-transmitting material in which a phosphor film is formed on the inner surface and enclosing a discharge gas, and a first internal electrode that is sealed at one end of the light-emitting tube and applies a high-frequency rectangular alternating voltage And a second internal electrode sealed at an end of the arc tube opposite to the first internal electrode, and an external electrode provided so as to be along the longitudinal direction of the arc tube. Further, the fluorescent lamp includes capacitive internal charge discharging means electrically connected to the second internal electrode.

[0014] A fluorescent lamp according to the present invention includes an arc tube made of a light-transmitting material in which a phosphor film is formed on the inner surface and enclosing a discharge gas, and a high-frequency rectangular alternating voltage sealed at one end of the arc tube. A first internal electrode to be applied, a second internal electrode sealed at the opposite end of the first internal electrode of the arc tube, and a capacitive electrically connected to the second internal electrode Internal charge discharging means and an external charge unit that is provided along the longitudinal direction of the arc tube at a predetermined distance from the arc tube. A partial electrode.

A liquid crystal display device according to the present invention includes a liquid crystal panel and a backlight device that illuminates the liquid crystal panel. The knocklight device includes the lamp lighting device described above.

The invention's effect

[0016] The present invention discharges residual charge during discharge through the capacitive internal charge discharging means to the outside of the arc tube, and controls the amount of residual charge inside the arc tube, thereby allowing polarity in dielectric barrier discharge. It is possible to lower the plasma conductivity during inversion and to make the discharge efficiency uniform over the entire length of the arc tube. As a result, it is possible to provide an efficient noble gas fluorescent lamp for backlight with uniform luminance distribution in the longitudinal direction of the arc tube.

Brief Description of Drawings

FIG. 1 is a perspective view of a rare gas fluorescent lamp according to Embodiment 1 of the present invention.

FIG. 2 is a graph showing the effect of the present invention.

FIG. 3 is a schematic diagram for explaining the discharge state of the rare gas fluorescent lamp of the present invention.

FIG. 4 is a schematic diagram showing an electrical circuit configuration according to the first embodiment of the present invention.

FIG. 5 is a schematic diagram showing a method for measuring capacitance in the present invention.

[Figure 6] Diagram showing an example of V-Q Lissajous in measuring capacitance

FIG. 7 is a diagram showing an example of a capacitance measurement result showing the effect of the present invention.

FIG. 8 is a perspective view of a liquid crystal backlight unit according to Embodiment 2 of the present invention.

FIG. 9 shows a configuration of a liquid crystal display device according to Embodiment 2 of the present invention.

[Figure 10] Diagram showing the configuration of a conventional rare gas fluorescent lamp

Explanation of symbols

[0018] 1, 101 Internal electrode

10 Noble gas fluorescent lamp

101a Internal electrode for driving

101b Internal charge adjustment internal electrode

2, 102 arc tube

3, 103 External electrode

104 Conductor member acting as internal charge adjustment means 200 Power supply circuit

250 lamp lighting device

300 LCD backlight unit

400 LCD panel

430 LCD panel drive circuit

450 knock light device

500 liquid crystal display

X Internal charge discharging means

Y pseudo lamp capacity

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0020] (Embodiment 1)

FIG. 1 is a diagram showing a configuration of a rare gas fluorescent lamp according to the first embodiment of the present invention. In FIG. 1, the arc tube 102 is a light-transmitting hard glass cylindrical tube such as borosilicate glass, and the inner surface has an excitation spectrum that is particularly strong in the vacuum ultraviolet region (mainly 200 nm or less). A selected three-wavelength phosphor film (not shown) is formed. Inside the arc tube 102, a rare gas mainly made of xenon is sealed as a discharge gas at a pressure of about 16 kPa at room temperature. Inner electrodes 101 (101a, 101b) of cup-shaped cold cathodes are hermetically sealed at both ends of the arc tube 102. The first and second internal electrodes 101 (101a, 101b) are made of a metal having a high melting point and high electrical conductivity such as nickel.

[0021] The arc tube 102 is separated from the external electrode 103 made of a substantially flat aluminum material by a spacer 105 made of an insulating material such as silicone resin. 3. Omm (however, the outer surface of the arc tube 102 and the external (The shortest distance from the electrode 103). The external electrode 103 has a high brightness reflective coating on its surface. Here, the substantially flat plate shape does not necessarily need to be a completely flat plate. For example, it is allowed to have a concave shape having a width at least about the diameter of the arc tube 102 and having a radius of curvature larger than the distance to the axis of the arc tube 102.

One of the internal electrodes 101 101a is used as a driving internal electrode. Internal drive Lighting is driven by applying a rectangular alternating voltage with a frequency of 20 kHz between the electrode 101a and the external electrode 103 from a lamp lighting power supply circuit (not shown in FIG. 1, see FIG. 4). In this case, it is desirable for safety reasons that the external electrode 103 is set to a reference potential (ground potential). When a voltage is applied, since the glass tube wall of the arc tube 102 acts as a charge barrier, a dielectric barrier discharge can be realized between the driving internal electrode 101a and the external electrode 103.

[0023] At the end opposite to the driving internal electrode 101a, the internal electrode for adjusting the internal charge of the cold cathode (hereinafter referred to as "adjusting internal electrode") is the same as the driving internal electrode 101a. ) 101b is sealed. The adjustment internal electrode 101b is electrically and physically connected to the conductor member 104 outside the arc tube 102, and operates as internal charge discharging means. The internal charge discharging means has a function of discharging charges that can be accumulated at the end of the arc tube 102. The conductor member 104 is a flat plate-like conductive member disposed in a plane parallel to the external electrode 103. Here, both the adjustment internal electrode 101b and the conductor member 104 are at a floating potential. Preferably, the conductor member 104 is made of an aluminum plate having an area of about lcm ² and the distance from the external electrode 103 is about 4.5 mm.

FIG. 2 shows the measurement result of the luminance distribution in the longitudinal direction of the rare gas fluorescent lamp of the first embodiment. In the figure, for comparison, a case of a conventional configuration including no conductor charge discharging means including the conductor member 104 and a case of the configuration of the present embodiment (the present invention) using the conductor member 104 are shown. Solid lines (curves Pl, P2) are conventional cases where the conductor member 104 is not connected, and broken lines (curves Ql, Q2) are cases where the conductor member 104 (area lcm ² ) is connected. When the applied voltage is 2. OkV, the conductor member 104 is not connected.

0-P

The luminance on the adjustment internal electrode 101a side is high, and the luminance on the adjustment internal electrode 101b side is low. In other words, it can be seen that the applied voltage is insufficient. On the other hand, when conductor member 104 is connected, almost uniform luminance distribution can be achieved even with the same applied voltage of 2. OkV.

0-P

I understand. In order to evaluate the brightness uniformity, the flat part of the tube brightness in Fig. 2 was fitted with a straight line and the inclination was found to be 0.0015 when the conductor member 104 was not connected. On the other hand, when the conductor member 104 was connected, it was improved to +0.0009. In visual evaluation, it was found that when the inclination was larger than ± 0.001, it started to feel light and dark. In other words, it is possible to adopt a simple configuration as in the first embodiment. Thus, it was found that the luminance distribution in the longitudinal direction of the rare gas fluorescent lamp can be made uniform without increasing the applied voltage.

Here, in order to understand such an effect, the progress of the dielectric barrier discharge between the driving internal electrode 101a and the external electrode 103 will be briefly described with reference to FIG. In FIG. 3, as an example, it can be considered that the same argument holds for the force indicating the state in which the potential of the driving internal electrode 101a is reversed in the positive direction and the phase in which the reverse is reversed.

[0026] When the applied voltage of the driving internal electrode 101a increases and the discharge gas breaks down, first, discharge is started in the vicinity of the driving internal electrode 101a having the highest electric field strength. Plasma is generated inside the arc tube 102 by the start of discharge. Positive and negative charges in the plasma (mainly ions and electrons) pass through the space in the arc tube 102 by the electric field between the driving inner electrode 101a and the outer electrode 103, and the driving inner electrode 101a and the outer electrode. The lamp current flows by drifting in the direction of 103 respectively. The charges (electrons) drifted to the external electrode 103 side are accumulated on the tube wall of the arc tube 102 because the tube wall of the arc tube 102 which is an insulator acts as a charge barrier. The accumulated charge neutralizes the electric field between the electrodes due to the electric field generated by itself, and therefore, the discharge in the discharge gas cannot be maintained in the vicinity of the driving internal electrode 101a where the discharge is first started, and the discharge starts. Stop.

[0027] As a result, the plasma generated by the initial discharge remained in the space without drifting (referred to as “residual charge”) 1S \, a state similar to the so-called “norse afterglow plasma” It exists. Since the plasma behaves as a conductor having a finite electrical resistance, the tip A of the residual charge becomes a pseudo internal electrode having a potential that is lower than the potential of the driving internal electrode 101a by a voltage drop due to the residual charge. .

[0028] On the other hand, in the region beyond the tip A of the residual charge, no electric charge is accumulated on the tube wall of the arc tube 102. Therefore, an electric field due to the potential difference between the tip A of the residual charge and the external electrode 103 is generated. Therefore, the discharge can be started. Therefore, the voltage at the tip A of the residual charge drops below the discharge start voltage due to the voltage drop in the plasma, and every minute distance in the longitudinal direction of the arc tube 102 until the tip A reaches the end of the arc tube 102. In addition, the discharge progresses while repeating the above process, and the residual charge plasma is stretched. This stretching speed is usually non- Since it is always fast (1 X 10 ⁶ m / sec or more), in the case of a frequency of about 20 kHz as used in the first embodiment, a Norse lamp current flows immediately after the polarity of the applied voltage is reversed. The half-cycle (25 microseconds) until the polarity is reversed again is a rest period in which almost no current flows.

[0029] Since the accumulated charge is maintained by the applied voltage until the polarity of the applied voltage is reversed again after the discharge is completed, an effective electric field force S is not applied in the arc tube 102. Become. However, since it takes time of several tens of microseconds or more to completely disappear (due to volume recombination and bipolar diffusion), a certain amount of residual charge is present at the next polarity inversion.

By the way, as described above, in the rare gas fluorescent lamp using xenon, the ultraviolet light that excites the phosphor is emitted when the xenon excimer dissociates from the resonance line of 147 nm emitted from the xenon excited atom. It consists of continuous radiation with a peak near 172 nm. In particular, it is important to improve the lamp efficiency that the continuous radiation from the excimer has high efficiency and it is effectively generated. An excimer is formed by a collision reaction (three-body collision process) between one xenon atom in an excited state and two xenon atoms in the ground state. Since xenon-excited atoms require higher energy for excitation than mercury used in general fluorescent lamps, the energy (electron temperature) of electrons in the plasma must be high in order to efficiently generate xenon-excited atoms. Therefore, the resonance line emission at 147 nm is emitted mainly in a Norse shape when the polarity of the applied voltage is reversed, in which electrons are accelerated by a high electric field.

[0031] On the other hand, since electrons do not intervene in the three-body collision process, excimer formation and 172 nm continuous emission continue even after the end of discharge. Rather, in the presence of electron current, once excited xenon excited atoms are easily ionized by collision with relatively low energy electrons (accumulated ionization), so excimer formation efficiency is high in plasma with high current density. Decreases. Therefore, in order to obtain continuous radiation from the excimer efficiently, the current density should be low.

[0032] As a result of applying the above discussion to the present invention to a rare gas fluorescent lamp configured as shown in Fig. 1, the luminance distribution in the longitudinal direction is uneven due to the following factors. The power to ignore S can be.

[0033] When the applied voltage is low, the opposite side of the driving internal electrode 101a contributes to the progress of discharge. As the plasma potential decreases, the luminance decreases. On the other hand, when the applied voltage is increased, the efficiency decreases due to excessive current in the vicinity of the driving internal electrode 101a. In other words, simply increasing the applied voltage to advance the discharge far will increase the current density in the vicinity of the driving internal electrode 101a, lowering the UV emission efficiency and lowering the brightness. It is. Furthermore, if a large amount of residual charge plasma exists at the time of polarity reversal of the applied voltage, the space inside the arc tube 102 is in a state of low electrical resistance, and the current density during discharge increases. In extreme cases, it is observed that the discharge contracts linearly and becomes streamer (fibrous). From the above discussion, in this state, the electron temperature is lowered, the xenon excitation efficiency is lowered, the cumulative ionization is dominant, and the ultraviolet radiation efficiency is lowered. In particular, at the end on the opposite side of the driving internal electrode 101a, the electric field strength is reduced due to excessive residual charges. Therefore, it is difficult to increase the luminance even if the applied voltage is increased, and the applied voltage must be further increased.

[0034] The lifetime of this residual charge is largely determined by the composition and pressure of the discharge gas. However, since the composition and gas pressure of the discharge gas also affect the luminous efficiency and lamp life, it cannot be determined independently. For this reason, in order to reduce the residual charge to a sufficiently small state when the polarity of the applied voltage at which the noise discharge occurs is reversed, it is necessary to wait for the residual charge to recombine and disappear. It is effective to lengthen the length. However, when the drive frequency is lowered, the number of discharges per unit time is reduced, and the light output is inevitably reduced, resulting in a decrease in light output as a lamp. For this reason, it is necessary to increase the number of lamps in order to secure the necessary amount of light, and it is impractical to significantly reduce the frequency! /.

Therefore, the inventors of the present application have studied a means for positively controlling the residual charge in the arc tube 102 without waiting for natural disappearance based on the consideration of the physical process as described above. As a result, the idea was to provide internal charge discharging means as in the present invention.

FIG. 4 is a diagram schematically showing the configuration of the rare gas fluorescent lamp shown in FIG. As shown in the figure, in the rare gas fluorescent lamp according to the present invention, since the flat conductor member 104 is set to a floating potential (not grounded) as a preferred embodiment, the conductor member 104 and the external electrode 103 are arranged in parallel. A plate capacitor Cx is formed, which operates as the capacitive internal charge adjustment means X. That is, residual charge plasma that has been stretched according to the process described above. When reaching the end of the arc tube 102, it contacts the internal electrode for adjustment 101b. Apparently from the plasma, outside the arc tube 102, it is connected in series with the plasma (the internal capacitance 101a for the drive and the lamp capacity Y that the plasma and the external electrode 103 produce are simulated via a plasma resistor). It appears that capacitor Cx is connected in parallel. For this reason, as much charge as the capacitance of the parallel plate capacitor Cx formed by the conductor member 104 and the external electrode 103 allows is discharged from the internal space of the arc tube 102 by being accumulated in the capacitor Cx. Become. As a result, a decrease in electric field strength can be suppressed even near the adjustment internal electrode 101b, and the luminance can be increased near the end on the adjustment internal electrode 101b side. In addition, since the discharge can be advanced even at a low applied voltage, it is possible to suppress a decrease in efficiency due to an increase in current density even in the vicinity of the driving internal electrode 101a. Therefore, the luminance distribution in the longitudinal direction can be made uniform with a lower driving voltage. Note that the potential of the conductor member 104 is preferably a floating potential without clipping to another potential. When the plasma is stretched, the potential of the conductor member 104 becomes equal to the plasma potential (strictly, there is a difference only by the sheath potential), so that the charge discharge is performed smoothly and smoothly as necessary. It becomes easier to balance.

[0037] In addition, the adjustment internal electrode 101b is connected to the conductor member 104 outside and is exposed to the inside of the arc tube 102, and the residual charge plasma in the arc tube 102 during the rest period and also during the progress of discharge. And maintain the same potential. Therefore, the discharge is limited to the dielectric barrier discharge between the driving internal electrode 101a and the external electrode 103, and the adjustment internal electrode 101b does not contribute to the discharge! /.

[0038] Further effects obtained by the configuration as in the first embodiment will be described with reference to Fig. 2 again.

In FIG. 2, when the applied voltage is 2.4 kV, in the conventional lamp not using the conductor member 104, the luminance is low near the drive internal electrode 101a as shown by the curve P1. The distribution is such that the luminance is higher at the end on the opposite side. The slope at this time worsens to +0.00169. It can be understood that this is because the applied voltage becomes excessive, and therefore, in the vicinity of the driving internal electrode 101a, a contracted discharge state is caused, and the ultraviolet light emission efficiency is remarkably lowered and the luminance is lowered. However, the lamp of the present invention in which the conductor member 104 is connected. Similarly, when 2.4 kV is applied, the overall luminance increases as shown by curve Q1, but the flatness of the luminance distribution is maintained. The value of the slope at this time was very good at +0.00000 65. In other words, in the conventional case where the conductor member 104 is not connected (see curve P1), the good range of the luminance gradient with respect to the applied voltage is narrow, and the luminance gradient changes continuously as the applied voltage changes. In the case of the present invention in which the conductor member 104 is connected (see curve Q1), a good luminance distribution can be maintained at a certain voltage or higher (approximately 2. OkVO-p or higher in this embodiment). This shows that the stability of the luminance distribution characteristics with respect to the applied voltage can be increased by introducing the conductor member 104 in the product design, which is an important advantage. In addition, when used as a TV backlight, even when control is performed to increase the luminance by increasing the applied voltage according to the video scene, the luminance distribution will not be disturbed. .

[0040] Further, according to the configuration of the first embodiment, the arc tube 102 in which the electrodes are sealed at both ends is created using a process for manufacturing a normal cold cathode fluorescent lamp, and the conductor is connected to the electrode at one end thereof. The adjustment internal electrode 101b may be formed by connecting the member 104, and the opposite electrode may be used as the drive internal electrode 101a. Compared to the case where a circuit element (for example, a capacitor with a high withstand voltage and a small capacity) is used as an internal charge discharging means, the above-described great effects can be obtained without a large process modification during mass production. it can. Therefore, the increase in cost can be minimized.

As a result of many experimental studies, the preferred internal charge discharging means in the present embodiment is that the conductor member 104 has a flat plate shape, the area thereof is lcm ² , and the distance from the external electrode 103 is about 4.5 mm. It was. The electric capacity in this case was about 0.2 pF from the measurement result. The method for measuring the electric capacity at this time will be described below.

As shown in FIG. 5, a power measuring capacitor 150 is inserted between the external electrode 103 and the ground terminal of the power supply circuit 200, and the voltage Vq between both ends thereof is measured. From the capacitance of the power measuring capacitor 150 and the measured Vq, the amount of charge accumulated in the external electrode 103 can be determined. Since this accumulated charge is an integral value of the current, if the graph of applied voltage V is plotted on the horizontal axis and the accumulated charge Q is plotted on the vertical axis (V-Q Lissajous), as shown in Figure 6, the lamp is charged and discharged. It becomes a figure with hysteresis. By calculating this area, the lamp power for one cycle of the voltage waveform can be determined. Maru. At this time, the slope when the upper side and the lower side of the figure are viewed as straight lines is a physical quantity obtained by dividing the amount of charge by the voltage, and thus is considered to represent the quantity corresponding to the capacity. However, this amount includes the influence of the current associated with the discharge when the lamp is lit, which is based only on the geometric capacity of the light emitting tube 102 and the external electrode 103. Therefore, in order to minimize the influence of the discharge, only the part immediately after the voltage inversion is taken out, and the slope C1 when the driving internal electrode 101a is inverted from the cathode to the anode and conversely when the inversion from the anode to the cathode is performed. The slope C2 was determined. As a result of many experiments, the values of C1 and C2 hardly change even when the applied voltage or frequency is changed. Therefore, it is assumed that the values reflect the geometric capacity of the lamp.

[0043] FIG. 7 shows the geometry of the case where the conductor member 104 (area lcm ² , distance 3 mm of the external electrode 103 force) is attached and the case where the conductor member 104 is not attached based on the configuration of the first embodiment. The results of measuring the static capacities C1 and C2 are shown. The error bar is the standard deviation of the measurement results for multiple samples. From FIG. 7, when the conductor member 104 is mounted, both Cl and C2 increase in value, and the increment can be seen as about 0.2 pF. As mentioned earlier, this is consistent with the value calculated assuming a parallel plate capacitor. The reason why the values of C1 and C2 are different is that the mobility (electrons or ions) varies depending on the polarity of the driving internal electrode 101a, so that the difference in mobility affects each of them.

Naturally, the necessary capacity Cx of the internal charge discharging means can be changed according to other conditions, and the dimensions of the conductor member 104 can be changed accordingly. By increasing the area of the conductor member 104 and reducing the distance from the external electrode 103, the capacity Cx of the internal charge discharging means increases, and the amount of charge that can be discharged increases. As a result, it is possible to obtain an effect of making the luminance distribution uniform even with a lower applied voltage.

However, the force S and the like simultaneously increase the discharge current, leading to a decrease in the luminous efficiency as a whole. For example, according to the results of experiments conducted by the inventors of the present invention in which the area was changed with the distance kept at 4.5 mm using this embodiment, the efficiency decreased by about 10% at an area of about 4 cm ² or more. On the other hand, when the area of the conductor member 104 is too small, it is naturally difficult to obtain the effect of making the luminance distribution uniform.

[0046] As a result of repeated experiments by the inventors of the present application in consideration of the length of the arc tube 102 and the distance between the arc tube 102 and the external electrode 103, the efficiency is reduced, the luminance in the longitudinal direction is made uniform, and the drive power is reduced. From the balance of the pressure suppression effect, the preferable range of the electric capacity Cx of the internal charge discharging means was in the range of 0.1 lpF to 10 pF. If it is smaller than this, the effect of making the luminance distribution uniform cannot be obtained, and if it is larger than this, the efficiency decreases, and the deterioration of characteristics such as flickering due to unstable light emission is seen. Such a suitable electric capacity can be arbitrarily realized by a combination of the area of the conductor member 104 and the distance to the external electrode 103 because the internal charge discharging means is a parallel plate capacitor.

[0047] The material of the conductor member 104 is not limited to aluminum as long as it is a metal.

In place of the conductor member 104, a capacitor element having a high withstand voltage having a capacity in the above-mentioned preferable range can be substituted although it is not general.

[0048] The force using a cup-shaped cold cathode for the internal electrode 101 is not necessarily limited to this shape. By making the shape simpler, the cost can be reduced, and an emitter material can be applied to reduce the loss due to cathode fall. Similarly, although the external electrode 103 is an aluminum flat plate with a high-brightness reflective coating in this embodiment, other configurations are possible as long as the material has sufficient electrical conductivity. It is. For example, it is possible to increase the front luminance by making the arc tube 102 a substantially paraboloid near the focal point. In addition, the surface of the external electrode 103 can be a diffusion surface.

[0049] (Embodiment 2)

FIG. 8 is a diagram showing a configuration of a light emitting portion of a liquid crystal backlight unit using the rare gas fluorescent lamp shown in the first embodiment.

A liquid crystal backlight unit 300 in FIG. 8 has a configuration in which a plurality of rare gas fluorescent lamps 10 shown in the first embodiment are connected in parallel. The arc tube 102 is directly supported by the spacer 105 in order to maintain a predetermined distance from the external electrode 103 (about 3 mm in the present embodiment). A support member 106 made of a dielectric material such as a resin block is inserted between the conductor member 104 of the arc tube 102 and the external electrode 103. The conductor member 104 is bonded to the upper surface of the support member 106 to determine the position of the arc tube 102. In this embodiment, since the support member 106 is made of an epoxy resin having a relative dielectric constant of about 3.0, the area of the conductor member 104 is almost equal to 1/3 compared to the case where the support member 106 is not inserted. The effect is obtained. In addition, when dielectric barrier discharge is used as in the rare gas fluorescent lamp of the present invention, the laser power supply circuit 200 sees the laser. The overall load on the amplifier is capacitive. Therefore, in the present invention, since the current flowing through each lamp is limited by the load capacity, it is different from a normal cold cathode lamp that shows negative characteristics in current and voltage! It is possible to turn on (drive) the lamp. Therefore, in this embodiment, the driving internal electrode 101a is connected to the common power supply line 108 through the connector 107 and driven by the single power supply circuit 200. On the other hand, the adjustment internal electrode 101b is independent for each lamp. This is to prevent current from concentrating on the previously lit lamp when the timing of discharge progress is shifted due to lamp variations.

In the present embodiment shown in FIG. 8, the number of power lamps shown in the case where eight lamps are turned on can be appropriately increased or decreased depending on the size of the television screen or the like.

[0052] As the material of the support member 106, it is possible to select an appropriate material in consideration of its electrical characteristics and aging deterioration characteristics. In that case, the area of the conductor member 104 and the distance from the external electrode 103 should be appropriately designed.

In the second embodiment, the external electrode 103 may be constituted by a force using an aluminum flat plate, for example, a substantially flat conductor independent for each arc tube 102. In this case, it is desirable that all independent external electrodes 103 have the same reference potential.

FIG. 9 shows a configuration of a liquid crystal display device using the liquid crystal backlight unit of the second embodiment. The liquid crystal display device 500 includes a liquid crystal panel 400, a liquid crystal panel drive circuit 430 that drives the liquid crystal panel according to an input image signal, and a backlight device 450 that illuminates the liquid crystal panel 400. The knock light device 450 includes, for example, the liquid crystal backlight unit 300 shown in the second embodiment. In the liquid crystal display device configured as described above, the backlight device 45 can illuminate the liquid crystal panel 400 with backlight light having a uniform luminance distribution in the lamp longitudinal direction. For this reason, it is possible to display a high-quality image without luminance unevenness on the entire screen. In addition, as shown in FIG. 2, the backlight device 450 can realize a uniform luminance distribution independent of voltage, and therefore, even when the liquid crystal display device is controlled to change the luminance for each scene, the backlight device 450 has a high luminance level. Image quality can be displayed.

Industrial applicability

[0055] The present invention provides a fluorescent lamp excellent in brightness uniformity and high efficiency without using mercury. And is useful as a liquid crystal backlight, particularly a liquid crystal backlight for a large-screen television.

Claims

The scope of the claims

[1] A lamp lighting device including a fluorescent lamp and a power supply circuit for supplying a driving voltage to the fluorescent lamp,

The fluorescent lamp is

An arc tube made of a translucent material having a phosphor film formed on the inner surface and enclosing a discharge gas; a first internal electrode sealed at one end of the arc tube to apply a high-frequency rectangular alternating voltage;

A second internal electrode sealed at an end of the arc tube opposite to the first internal electrode;

An external electrode provided along the longitudinal direction of the arc tube;

A capacitive internal charge discharging means electrically connected to the second internal electrode,

A lamp lighting device characterized by that.

[2] The lamp lighting device according to claim 1, wherein the capacitance value of the internal charge discharging means is in the range of not less than 0.1 lpF and not more than 10 pF.

[3] The lamp lighting device according to [1], wherein the internal charge discharging means is a conductor member disposed opposite to the external electrode and placed at a floating potential.

4. The lamp lighting device according to claim 3, wherein a support member made of a dielectric is provided between the external electrode and the conductor member.

5. The lamp lighting device according to claim 1, wherein a plurality of the fluorescent lamps are arranged.

6. The lamp lighting device according to claim 5, wherein the internal charge discharging means of each of the plurality of fluorescent lamps is electrically separated.

[7] An arc tube made of a translucent material in which a phosphor film is formed on the inner surface and a discharge gas is enclosed;

A first internal electrode sealed at one end of the arc tube and applying a high frequency rectangular alternating voltage;

A second internal electrode sealed at an end of the arc tube opposite to the first internal electrode; An external electrode provided along the longitudinal direction of the arc tube;

A fluorescent lamp comprising: capacitive internal charge discharging means electrically connected to the second internal electrode.

A liquid crystal panel, and a backlight device that illuminates the liquid crystal panel, wherein the backlight device includes the lamp lighting device according to claim 1.